Prosthetic hand system

Abstract

A prosthetic hand structure including at least one mechanical finger having a metacarpal support and a proximal stiff link connected to the metacarpal support by a proximal cylindrical joint. The mechanical finger includes a transmission member connected to the proximal stiff link. The transmission member includes a worm screw integral to the proximal stiff link. The transmission member includes a flexible rack having a first end portion, pivotally connected to the metacarpal support, and a second end portion arranged to engage with the threaded profile of the worm screw at an engagement zone of the flexible rack. The structure also includes an actuator mounted to the mechanical finger and to actuate the worm screw, causing it to rotate about its rotation axis, in such a way that, when the actuator moves the worm screw, the mechanical finger extends or flexes.

What is claimed: 
     
       1. A prosthetic hand structure, comprising:
 at least one mechanical finger having a metacarpal support, a proximal stiff link connected to the metacarpal support by a proximal cylindrical joint, the proximal stiff link arranged for carrying out a rotation of the proximal stiff link of a first predetermined amplitude with respect to the metacarpal support about an axis of the proximal cylindrical joint, said at least one mechanical finger including a distal stiff link connected to the proximal stiff link by a distal cylindrical joint, the distal stiff link being arranged for carrying out a rotation of the distal stiff link of a second predetermined amplitude with respect to the proximal stiff link about an axis of the distal cylindrical joint; 
 a transmission member connected to the proximal stiff link, the transmission member arranged to actuate the proximal stiff link in order to cause the rotation of the proximal stiff link of the first predetermined amplitude, the transmission member comprising a worm screw having a threaded profile, the worm screw being integral with the proximal stiff link and arranged for carrying out a rotation of the worm screw about a longitudinal axis of the worm screw, the transmission member further comprising a flexible rack having a first end portion pivotally connected to the metacarpal support and a second end portion arranged to engage with a thread of the worm screw at an engagement zone of the flexible rack, wherein the flexible rack is configured to buckle such that compressive loads are not transferred integrally to the metacarpal support, and wherein the second end portion of the flexible rack is configured to translate along a direction substantially parallel to an axis of the worm screw, as the transmission member actuates the proximal stiff link, wherein in distancing the engagement zone away from the first end portion, the second end portion extends into the distal stiff link; 
 an actuator mounted to said at least one mechanical finger, the actuator arranged to actuate the worm screw of the transmission member to obtain the rotation of the worm screw about the longitudinal axis of the worm screw, in such a way that, when the actuator actuates the worm screw, there is a moving-away movement of the engagement zone from the first end portion, se wherein the second end portion of the flexible rack extends into the distal stiff link, or an approaching movement of the engagement zone to the first end portion, causing the rotation of the proximal stiff link of the first predetermined amplitude, in a direction of rotation, or in an opposite direction of rotation, of the proximal stiff link about the axis of the proximal cylindrical joint, the rotation of the proximal stiff link of the first predetermined amplitude corresponding to an extension or flexion movement of said at least one mechanical finger; 
 at least one feedback position sensor associated with said at least one mechanical finger, said at least one feedback position sensor being configured to measure a position of the proximal stiff link with respect to the metacarpal support for determining in real time an amplitude of rotation of the proximal stiff link, the feedback position sensor being configured to generate a corresponding feedback signal; and 
 a control unit connected to the feedback position sensor to receive the feedback signal, the control unit being configured to analyze the feedback signal and to operate the actuator to actuate the worm screw until the amplitude determined in real time meets the first predetermined amplitude. 
 
     
     
       2. The prosthetic hand structure of  claim 1 , wherein the rotation of the proximal stiff link of the first predetermined amplitude lies in a plane substantially orthogonal to the axis of the proximal cylindrical joint. 
     
     
       3. The prosthetic hand structure of  claim 2 , wherein the worm screw is adapted to carry out a rotation about a rotation axis of the worm screw, the rotation axis of the worm screw arranged in the plane substantially orthogonal to the axis of the proximal cylindrical joint. 
     
     
       4. The prosthetic hand structure of  claim 1 , wherein said at least one mechanical finger includes a distal stiff link connected to the proximal stiff link by a distal cylindrical joint, the distal stiff link being arranged for carrying out a rotation of the distal stiff link of the second predetermined amplitude with respect to the proximal stiff link about an axis of the distal cylindrical joint. 
     
     
       5. The prosthetic hand structure of  claim 4 , wherein the distal cylindrical joint is under-actuated by mechanical reduction gears or a belt. 
     
     
       6. The prosthetic hand structure of  claim 1 , wherein said at least one mechanical figure comprises a plurality of mechanical fingers including a mechanical finger for use as a thumb, the prosthetic hand structure further comprising: a metacarpal base, the metacarpal support of each mechanical finger of the plurality of the plurality of mechanical figures being connected to the metacarpal base, wherein the mechanical finger for use as the thumb is connected to the metacarpal base by a rotational joint to provide to the mechanical finger for use as the thumb an abduction or adduction degree of freedom. 
     
     
       7. The prosthetic hand structure of  claim 1 , wherein the feedback position sensor is a Hall-effect sensor. 
     
     
       8. The prosthetic hand structure of  claim 1 , further comprising at least one myoelectric sensor arranged, in use, in contact with a stump of a patient, the myoelectric sensor configured to measure a voltage associated with activation of an agonist or antagonist muscle of the stump of the patient and to generate a myoelectric signal. 
     
     
       9. The prosthetic hand structure of  claim 8 , further comprising a plurality of force sensors arranged, in use, in contact with the stump of the patient and distributed on a predetermined surface of the stump, the plurality of force sensors configured to measure a plurality of pressure data corresponding to a predetermined muscle configuration achieved by the patient and to generate at least one pressure distribution signal indicative of the plurality of pressure data measured on the stump. 
     
     
       10. The prosthetic hand structure of  claim 9 , wherein the control unit is configured to analyze the myoelectric signal and the pressure distribution signal and to carry out a selection of a predetermined working configuration among a plurality of possible predetermined working configurations, the control unit arranged to operate the actuator, to obtain the selected working configuration. 
     
     
       11. The prosthetic hand structure of  claim 10 , wherein the control unit performs the selection among the plurality of possible predetermined working configurations comparing the myoelectric signal and the pressure distribution signal predetermined by the myoelectric sensor and the plurality of force sensors with a plurality of signals associated with predetermined working configurations. 
     
     
       12. The prosthetic hand structure of  claim 11 , further comprising at least one inertial sensor selected from the group consisting of:
 an inertial sensor configured to measure a spatial orientation of the prosthetic hand structure with respect to a predetermined direction, to generate a corresponding spatial position signal, and to transmit the spatial position signal to the control unit; and 
 an inertial sensor configured to measure at least one linear speed, angular speed, or acceleration of the prosthetic hand structure, to generate a corresponding kinematic signal, and to transmit the kinematic signal to the control unit. 
 
     
     
       13. The prosthetic hand structure, of  claim 12 , wherein the control unit is arranged to carry out the selection of possible working configurations also on the basis of the spatial position signal or the kinematic signal.